CN104821347A - Lift-off method - Google Patents

Abstract

The present invention provides a peeling method capable of reliably peeling off an epitaxial substrate without degrading the quality of an optical device. The optical device layer of the optical device wafer, in which the optical device layer is laminated on the front surface of the epitaxial substrate via a buffer layer, is transferred to the transfer substrate by using a lift-off method. The composite substrate is formed by bonding and transferring the substrate by bonding agent; the buffer layer destruction step is to irradiate the buffer layer from the back side of the epitaxial substrate of the composite substrate with laser light having a wavelength that is transparent to the epitaxial substrate and has absorptivity to the buffer layer , to destroy the buffer layer; and the optical device layer transfer process, peeling off the epitaxial substrate of the composite substrate that has been subjected to the buffer layer damage process, transferring the optical device layer to the transfer substrate, and in the buffer layer damage process, the composite substrate The buffer layer is irradiated with laser light by heating to relax the springback generated on the epitaxial substrate and the transfer substrate.

Description

Stripping method

technical field

The present invention relates to a lift-off method for transferring an optical device layer of an optical device wafer in which an optical device layer is laminated on the front surface of an epitaxial substrate such as a sapphire substrate or silicon carbide through a buffer layer to a transfer substrate.

Background technique

In the optical device manufacturing process, an optical device layer composed of an n-type semiconductor layer and a p-type semiconductor layer is stacked on the front surface of a substantially disc-shaped sapphire substrate or an epitaxial substrate such as silicon carbide through a buffer layer. The semiconductor layer and the p-type semiconductor layer are made of GaN (gallium nitride) or INGaP (indium gallium phosphide) or ALGaN (aluminum gallium nitride), on multiple regions divided by a plurality of dicing lines formed in a grid pattern Optical devices such as light-emitting diodes and laser diodes are formed and constitute an optical device wafer. Then, the optical device wafer is divided along the dicing lines to manufacture individual optical devices.

In addition, the following Patent Document 1 discloses a manufacturing method called lift-off, in which the optical device layer of an optical device wafer is transferred to a Mo, Cu, or Si substrate for the purpose of improving the brightness of the optical device or improving the cooling. etc. on the transfer substrate.

Lift-off is a technique in which a transfer substrate is bonded to the optical device layer side of the optical device wafer via a bonding metal layer such as AuSn (gold tin), and the back surface of the epitaxial substrate is irradiated through the epitaxial substrate to irradiate the buffer layer. The absorbed laser light of wavelength (for example, 257nm) destroys the buffer layer, peels the epitaxial substrate from the optical device layer, and transfers the optical device layer to the transfer substrate.

Patent Document 1 Japanese Patent Application Laid-Open No. 2004-72052

However, when the optical device layer side of the optical device wafer is bonded with the transfer substrate through the bonding metal layer to form a composite substrate, the optical device wafer and the transfer substrate are heated to about 250° C. When the difference in thermal expansion coefficients of the substrates is transferred, the composite substrate is slightly bent at normal temperature. Therefore, when the buffer layer is damaged by irradiation of laser light, peeling occurs in the region not irradiated with laser light due to springback of the epitaxial substrate and the transfer substrate, thereby destroying the optical device layer and degrading the quality of the optical device.

Contents of the invention

The present invention has been made in view of the above circumstances, and its main technical subject is to provide a peeling method that can reliably peel off an epitaxial substrate without degrading the quality of an optical device.

In order to solve the above-mentioned main technical problems, the present invention provides a peeling method, which transfers the optical device layer of the optical device wafer on which the optical device layer is laminated on the front of the epitaxial substrate via a buffer layer to the transfer substrate, which is characterized in that it includes: Composite substrate forming process, on the front side of the optical device layer of the optical device wafer, the composite substrate is formed by bonding and transferring the substrate by means of bonding agent; the buffer layer destruction process, irradiating the epitaxial substrate from the back side of the epitaxial substrate of the composite substrate to the buffer layer has The buffer layer is destroyed by laser light of a wavelength that is transparent and absorptive to the buffer layer; and the optical device layer transfer process is performed by peeling off the epitaxial substrate of the composite substrate that has been subjected to the buffer layer destruction process, and the optical device The layer is transferred to the transfer substrate, and in this buffer layer destruction step, the composite substrate is heated to relieve springback generated on the epitaxial substrate and the transfer substrate, and the buffer layer is irradiated with laser light.

In the buffer layer breaking step, the temperature for heating the composite substrate is set to 100°C to 500°C.

In the peeling method of the present invention, before the buffer layer is irradiated with laser light having a wavelength that is transparent to the epitaxial substrate and absorbs to the buffer layer from the back side of the epitaxial substrate of the composite substrate in the buffer layer destroying step, recombination is performed. In the substrate heating process, specifically, the composite substrate is heated to alleviate the springback generated on the epitaxial substrate and the transfer substrate constituting the slightly curved composite substrate at room temperature, so that springback of the epitaxial substrate and the transfer substrate does not occur, so Can reliably destroy the buffer layer. In the optical device layer transfer process of peeling off the epitaxial substrate of the composite substrate and transferring the optical device layer onto the transfer substrate, the buffer layer will not be peeled off in the region where the buffer layer is not damaged. Therefore, the problem of delamination of the optical device layer due to peeling occurring in the region where the buffer layer is not damaged, resulting in a decrease in the quality of the optical device is eliminated.

Description of drawings

1 is a perspective view and an enlarged cross-sectional view of main parts of an optical device wafer on which an optical device layer is formed, which is transferred to a transfer substrate by a lift-off method of the present invention.

Fig. 2 is an explanatory diagram of a composite substrate forming step in the peeling method of the present invention.

3 is a perspective view of a laser processing apparatus for carrying out a buffer layer destruction step and an optical device layer transfer step in the lift-off method of the present invention.

FIG. 4 is a cross-sectional view of a chuck table installed in the laser processing apparatus shown in FIG. 3 .

Fig. 5 is a cross-sectional view showing another embodiment of the chuck table provided in the laser processing apparatus shown in Fig. 3 .

Fig. 6 is an explanatory diagram of a buffer layer destruction step in the peeling method of the present invention.

7 is an explanatory diagram of an epitaxial substrate adsorption step in the optical device layer transfer step of the lift-off method of the present invention.

FIG. 8 is an explanatory diagram of a peeling step in an optical device layer transfer step of the peeling method of the present invention.

Label description

2: Optical device chip

21: Epitaxial substrate

22: Optical device layer

23: buffer layer

3: Relocation of the substrate

4: Join the metal layer

200: composite substrate

5: Laser processing device

6: Chuck table mechanism

66: chuck table

662: Porous Ceramic Heater

663: Power circuit

666: Rubber Heater

67: Machining feed components

7: Laser light irradiation unit support mechanism

72: Movable support base

8: Laser light irradiates the component

83: Focus point position adjustment member

84: Concentrator

85: camera components

9: Peeling mechanism

91: Adsorption components

912a, 912b, 912c: suction pads

Detailed ways

Hereinafter, preferred embodiments of the peeling method of the present invention will be described in detail with reference to the drawings.

(a) and (b) of FIG. 1 show a perspective view and an enlarged cross-sectional view of main parts of an optical device wafer formed with an optical device layer transferred to a transfer substrate by the lift-off method of the present invention.

The optical device wafer 2 shown in (a) and (b) of FIG. The optical device layer 22 composed of the n-type gallium nitride semiconductor layer 221 and the p-type gallium nitride semiconductor layer 222 is formed by the epitaxial growth method. In addition, when the optical device layer 22 composed of the n-type gallium nitride semiconductor layer 221 and the p-type gallium nitride semiconductor layer 222 is stacked by the epitaxial growth method on the front surface of the epitaxial substrate 21, the front surface 21a of the epitaxial substrate 21 and the formation of the optical device layer A buffer layer 23 made of gallium nitride (GaN) and having a thickness of, for example, 1 μm is formed between the n-type gallium nitride semiconductor layers 221 of the layer 22 . The optical device wafer 2 configured as above is formed such that the thickness of the optical device layer 22 is, for example, 10 μm in the present embodiment. In addition, in the optical device layer 22 , as shown in FIG. 1( a ), optical devices 224 are formed in a plurality of regions divided by a plurality of dicing lines 223 formed in a lattice.

As described above, in order to peel the epitaxial substrate 21 of the optical device wafer 2 from the optical device layer 22 and transfer it to the transfer substrate, it is necessary to perform a composite substrate forming process in which the transfer substrate is bonded to the front surface 22 a of the optical device layer 22 . to form a composite substrate. That is, as shown in (a), (b) and (c) of FIG. A bonding metal layer 4 made of AuSn) as a bonding agent is bonded to a transfer substrate 3 made of a copper substrate having a thickness of 1 mm. In addition, molybdenum (Mo), copper (Cu), silicon (Si), etc. can be used as the transfer substrate 3, and gold (Au), platinum (Pt), chromium ( Cr), indium (In), palladium (Pd), etc. In this composite substrate forming step, the above-mentioned bonding metal is vapor-deposited on the front surface 22a of the optical device layer 22 formed on the front surface 21a of the epitaxial substrate 21 or the front surface 3a of the transfer substrate 3 to form a bonding metal layer 4 with a thickness of about 3 μm. The bonding metal layer 4 is pressure-bonded to face the front surface 3 a of the transfer substrate 3 or the front surface 22 a of the optical device layer 22 , and is bonded to the front surface 22 a of the optical device layer 22 constituting the optical device wafer 2 via the bonding metal layer 4 . The composite substrate 200 is formed by transferring the front surface 3 a of the substrate 3 . In addition, in the composite substrate forming process, when the transfer substrate 3 is bonded to the front surface 22a of the optical device layer 22 formed on the front surface 21a of the epitaxial substrate 21 to form the composite substrate 200, the epitaxial substrate 21 and the transfer substrate 3 are heated to 250°C. Therefore, the composite substrate 200 is slightly warped at normal temperature based on the difference in thermal expansion coefficient between the epitaxial substrate 21 and the transfer substrate 3 .

As described above, after the front surface 22a of the optical device layer 22 constituting the optical device wafer 2 is bonded to the front surface 3a of the transfer substrate 3 via the bonding metal layer 4 to form the composite substrate 200, the buffer layer destruction process is performed, that is, the composite substrate 200 is formed. The back side of the epitaxial substrate 21 of the substrate 200 irradiates the buffer layer 23 with laser light having a wavelength that is transparent to the epitaxial substrate 21 and absorbs to the buffer layer 23 to destroy the buffer layer 23 . In the buffer layer destruction process, it implements using the laser processing apparatus shown in FIG. The laser processing device 5 shown in FIG. 3 has: a stationary base 50; On the seat 50, it is used to hold the workpiece; the laser beam irradiation unit support mechanism 7 is movable in the index feed direction (Y-axis direction) shown by the arrow Y perpendicular to the above-mentioned X-axis direction. Arranged on the stationary base 50; and the laser beam irradiation member 8, which is arranged on the laser beam irradiation unit supporting mechanism in a manner capable of moving in the focusing point position adjustment direction (Z-axis direction) shown by arrow Z 7 on.

The above-mentioned chuck table mechanism 6 has: guide rails 61, 61 arranged parallel to the stationary base 50 along the X-axis direction; On the guide rails 61, 61; the second slide block 63 is arranged on the guide rails 621, 621 arranged on the upper surface of the first slide block 62 so as to be movable in the Y-axis direction; the cover stand 65, on which The second slide block 63 is supported by the cylindrical member 64 ; and the chuck table 66 as a workpiece holding member. As shown in FIG. 4 , the chuck table 66 is composed of a chuck table main body 661 and a porous ceramic heater 662 working as a suction and holding member, and the porous ceramic heater 662 is arranged in the holding area 660 of the chuck table main body 661 up and breathable. The chuck table main body 661 is composed of a disc-shaped holding portion 661a and a rotating shaft portion 661b protruding from the lower surface of this 661a, and is integrally formed of a metal material such as stainless steel or ceramics. A circular fitting recess 661c is provided in the holding region 660 on the upper surface of the holding portion 661a. The fitting recess 661c is provided with an annular support frame 661d, and the porous ceramic heater 662 is placed on the outer peripheral portion of the bottom surface of the support frame 661d. The holding portion 611a and the rotating shaft portion 611b forming the chuck table main body 661 are provided with a suction passage 611e opened in the fitting recessed portion 661c.

The above-mentioned porous ceramic heater 662 working as a suction and holding member is fitted into the fitting recess 661c formed on the upper surface of the holding portion 661a of the chuck table main body 661 and placed on the ring-shaped support frame 661d. The porous ceramic heater 662 The outer peripheral surface of the fitting recess 661a is bonded with an appropriate adhesive. Thus, the porous ceramic heater 662 fitted into the fitting recess 661c provided in the holding portion 661a of the chuck table main body 661 is configured such that its upper surface is flush with the upper surface of the holding portion 661a.

The suction passage 661e formed in the chuck table body 661 of the chuck table 66 configured as above is connected to a suction member (not shown). Therefore, the workpiece is placed on the porous ceramic heater 662 provided on the holding area 660 of the chuck table main body 661, and the suction member (not shown) is activated, so that negative pressure acts on the porous ceramic heater through the suction passage 661e. The upper surface of the porous ceramic heater 662 attracts and holds the workpiece on the upper surface of the porous ceramic heater 662 .

In addition, a porous ceramic heater 662 constituting the chuck table 66 is connected to a power supply circuit 663 . Therefore, the porous ceramic heater 662 is heated to a predetermined temperature by applying electric power from the power supply circuit 663 . In addition, the heating temperature of the porous ceramic heater 662 is preferably 100 to 500°C.

Next, another embodiment of the chuck table 66 will be described with reference to FIG. 5 . In the chuck table 66 shown in FIG. 5 , the chuck table main body 661 is composed of an upper member 664 and a lower member 665 , and a rubber heater 666 is arranged between the upper member 664 and the lower member 665 . The upper member 664 is provided with a negative pressure chamber 664a, and a plurality of suction holes 664b that communicate with the negative pressure chamber 664a and open on the upper surface and a communication hole 664c that opens on the lower surface are formed. Moreover, the above-mentioned rotation shaft part 661b is provided in the lower surface of the lower member 665. As shown in FIG. In addition, a communication passage 666a is provided at the center of the rubber heater 666, and the communication passage 666a communicates with the communication hole 664c formed in the upper member 664 and the suction passage 661e formed in the lower member 665 and the rotation shaft portion 661b. The rubber heater 666 constituting the chuck table 66 configured as above is connected to a power circuit and heated to 100 to 500° C. as in the embodiment shown in FIG. 4 .

Continuing the description with reference to FIG. 3 , the chuck table 66 configured as above is rotated by a pulse motor (not shown) arranged in the cylindrical member 64 . In addition, the chuck table mechanism 6 has a processing feed member 67 for moving the first slide block 62 in the X-axis direction along the guide rails 61, 61, and a processing feed member 67 for moving the second slide block 63 in the Y-axis direction along the guide rails 621, 621. The first index feed member 68 that moves upward. In addition, the processing feed member 67 and the 1st index feed member 68 are comprised by the well-known ball screw mechanism.

The above-mentioned laser beam irradiation unit support mechanism 7 has a pair of guide rails 71, 71 arranged in parallel on the stationary base 50 along the Y-axis direction, and is arranged on the guide rails 71, 71 so as to be movable in the Y-axis direction. The movable support base 72. The movable support base 72 is configured to have a movable support portion 721 movably arranged on the guide rails 71, 71, and a mounting portion 722 attached to the movable support portion 721, and is configured by a ball screw mechanism. The second index feeding member 73 moves in the Y-axis direction along the guide rails 71 , 71 .

The laser beam irradiation member 8 has a unit holder 81 and a housing 82 attached to the unit holder 81 . The unit holder 81 is supported so as to be movable in the Z-axis direction along guide rails 723 , 723 provided on the mounting portion 722 of the movable support base 72 . The unit holder 81 supported so as to be movable along the guide rails 723 , 723 as described above moves in the Z-axis direction by the focal point position adjustment member 83 constituted by a ball screw mechanism.

The laser beam irradiation member 8 has a cylindrical case 82 fixed to the unit holder 81 and extending substantially horizontally. A pulsed laser beam oscillating unit having a pulsed laser beam oscillator and a repetition rate setting unit (not shown) is provided in the casing 82 . A concentrator 84 for converging the pulsed laser beam oscillated by the pulsed laser beam oscillating member is attached to the front end portion of the housing 82 . An imaging member 85 for imaging the workpiece held on the chuck table 66 by the laser beam irradiation member 8 is arranged at the front end portion of the housing 82 . The imaging means 85 is composed of optical means such as a microscope and a CCD camera, and transmits image signals obtained by imaging to a control means (not shown).

The laser processing apparatus 5 has a peeling mechanism 9 for peeling the epitaxial substrate 21 constituting the above-mentioned optical device wafer 2 from the optical device layer 22 . The peeling mechanism 9 is configured to include: a suction member 91 that sucks the epitaxial substrate 21 in a state where the optical device wafer 2 held on the chuck table 66 is positioned at the peeling position; and a support member 92 that pulls the suction member 91 It is supported so as to be movable in the vertical direction, and this peeling mechanism 9 is arranged on one side of the chuck table mechanism 6 . The suction member 91 includes a holding member 911 and a plurality of (three in the illustrated embodiment) suction pads 912a, 912b, 912c attached to the lower side of the holding member 911. The suction pads 912a, 912b, 912c It is connected to an attraction member not shown.

In the step of destroying the buffer layer, that is, using the above-mentioned laser processing device 5 to irradiate the buffer layer 23 from the back side of the epitaxial substrate 21 of the composite substrate 200, laser light having a wavelength that is transparent to the epitaxial substrate 21 and has absorptivity to the buffer layer 23 Light, when destroying the buffer layer 23, need to be on the upper surface of the porous ceramic heater 662 that constitutes the chuck table 66 shown in Fig. The transfer substrate 3 side of the above-mentioned composite substrate 200 is placed on the upper surface of the upper member 664 of the main body 661 . Then, power is applied to the porous ceramic heater 662 or the rubber heater 666 constituting the chuck table 66 and heated to 100 to 500°C. As a result, the composite substrate 200 sucked and held on the chuck table 66 is heated to 100 to 500° C. (composite substrate heating step). Therefore, the springback generated in the epitaxial substrate 21 and the transfer substrate 3 constituting the composite substrate 200 which are slightly bent at normal temperature is alleviated.

After the composite substrate heating step described above is performed, a suction member (not shown) is activated to suck and hold the composite substrate 200 on the chuck table 66 (wafer holding step). Therefore, the back surface 21b of the epitaxial substrate 21 constituting the optical device wafer 2 of the composite substrate 200 sucked and held on the chuck table 66 becomes the upper side. As above, after the composite substrate 200 is sucked and held on the chuck table 66 , the process feeding member 67 is activated to move the chuck table 66 to the laser beam irradiation area where the condenser 84 of the laser beam irradiation member 8 is located. Then, as shown in FIG. 6( a ), one end (the left end in FIG. 6( a )) of the epitaxial substrate 21 of the optical device wafer 2 constituting the composite substrate 200 held on the chuck table 66 (the left end in FIG. 6( a )) is positioned on the laser beam. The light irradiates directly below the condenser 84 of the member 8 . Next, start the laser beam irradiating member 8, and irradiate the buffer layer 23 with a pulsed laser beam with a wavelength that is transparent to sapphire and absorbing to the buffer layer 23 from the concentrator 84, and the chuck table 66 is positioned at the position shown in FIG. 6 . (a) moves at a predetermined machining feed rate in the direction indicated by the arrow X1. Then, as shown in (c) of FIG. 6 , when the other end of the epitaxial substrate 21 (the right end in (c) of FIG. 6 ) reaches the irradiation position of the light collector 84 of the laser beam irradiation member 8, the pulsed laser light is stopped. The irradiation of the light stops the movement of the chuck table 66 . This buffer layer destruction step is performed in a region corresponding to the entire surface of the buffer layer 23 .

In addition, the above-mentioned buffer layer destruction step may be carried out by positioning the light concentrator 84 on the outermost periphery of the epitaxial substrate 21, rotating the chuck table 66, and moving the light concentrator 84 toward the center so as to cover the entire buffer layer 23. The surface is irradiated with pulsed laser light.

The processing conditions of the above buffer layer breaking step are set as follows.

The buffer layer destruction step is performed based on the above processing conditions, whereby the buffer layer 23 is destroyed. In the above-mentioned buffer layer destruction step, before the laser beam irradiation member 8 is activated, and the buffer layer 23 is irradiated with pulsed laser beams having a wavelength that is transparent to sapphire and absorbs to the buffer layer 23 from the concentrator 84, recombination is performed. In the substrate heating step, the composite substrate 200 sucked and held on the chuck table 66 is heated to relieve the springback generated on the epitaxial substrate 21 and the transfer substrate 3 constituting the composite substrate 200 which are slightly bent at room temperature. Since springback of the epitaxial substrate 21 and the transfer substrate 3 occurs, the buffer layer 23 can be reliably broken.

After performing the buffer layer destruction step described above, an optical device layer transfer step of peeling off the epitaxial substrate 21 of the composite substrate 200 and transferring the optical device layer 22 onto the transfer substrate 3 is performed. That is, the chuck table 66 is moved to the peeling position where the peeling mechanism 9 is disposed, and the composite substrate 200 held on the chuck table 66 is positioned directly below the adsorption member 91 as shown in FIG. 7( a ). Then, as shown in FIG. 7(b), the suction member 91 is lowered, the suction pads 912a, 912b, and 912c are brought into contact with the back surface 21b of the epitaxial substrate 21, and the suction member (not shown) is activated, so that the suction pads 912a, 912b , 912c suction the back surface 21b of the epitaxial substrate 21 (epitaxial substrate suction step).

After the above-mentioned epitaxial substrate adsorption step is carried out, a peeling step is carried out, that is, the suction pads 912a, 912b, 912c having adsorbed the epitaxial substrate 21 are moved in a direction away from the epitaxial substrate 21 to peel off the epitaxial substrate 21, and the optical device layer 22 is removed. Set on the transfer substrate 3 . That is, as shown in (b) of FIG. 7 above, from the state where the epitaxial substrate suction step has been performed, the suction member 91 is moved upward as shown in FIG. . As a result, the optical device layer 22 is transferred onto the transfer substrate 3 . The buffer layer 23 of the composite substrate 200 subjected to the optical device layer transfer process consisting of the above-mentioned epitaxial substrate adsorption process and the peeling process is reliably broken in the above-mentioned buffer layer breaking process, so that the undamaged buffer layer 23 will not be damaged. The area is stripped. Therefore, the problem that the optical device layer 22 is damaged by peeling off in an undamaged region of the buffer layer 23 , resulting in a reduction in the quality of the optical device, is eliminated.

Claims (2)

1. a stripping means, establish substrate by being transferred to move across the optical device layer of the optical device wafer of the stacked optical device layer of resilient coating in the front of epitaxial substrate, the feature of this stripping means is, comprising:

Composite base plate formation process, engages to move by means of cement in the front of the optical device layer of optical device wafer and establishes substrate and form composite base plate;

Resilient coating destroys operation, and from the rear side of the epitaxial substrate of composite base plate to resilient coating, irradiation has permeability to epitaxial substrate and resilient coating had to the laser beam of absorbefacient wavelength, destroys resilient coating; And

Optical device layer is moved and is established operation, peels off, optical device layer moved to establish and establish substrate to moving the epitaxial substrate being implemented this resilient coating and destroying the composite base plate after operation,

Destroy in operation at this resilient coating, composite base plate is heated, relax and result from epitaxial substrate and move the resilience of establishing on substrate, to resilient coating irradiating laser light.

2. stripping means according to claim 1, wherein,

Destroy in operation at this resilient coating, 100 DEG C ~ 500 DEG C are set to the temperature that composite base plate heats.